For the purpose of integrating RF equipment, it has been common practice in the art to interconnect modules by means of coaxial cables, or by placing a large number of hybrid integrated circuits inside a large module. Disadvantageously, however, the use of coaxial cable involves a large volume and weight, while incorporating many circuits in a single large module lowers its reliability, and results in a non-standard module which may also be difficult to seal hermetically.
A scheme developed by the Assignee of the present application for eliminating the shortcomings of these conventional techniques involves the use of short links of fine (e.g. No. 36) wire which are surrounded by a suitable dielectric covering or jacket (e.g. Teflon) and which overlie one surface of a conductive planar module board. The modules are mounted on the opposite side of the board and pin connections thereto extend through apertures in the board so that the links of wire may be connected to the pins. A thin sheet of conductive foil, such as aluminum foil, is pressed onto the board, so that the wires effectively create microwave transmission "tunnels" in the foil. This transmission medium, termed "tunneline", allows the use of individualized, standard off-the-shelf modules and eliminates the large volume and weight associated with coaxial cable interconnects. Moreover because of its flexibility it may be employed in conformal structures that do not readily lend themselves to use with other types of transmission media, such as stripline or microstrip, and offers packaging advantages over conventional transmission structures in terms of component density, isolation, heat transfer and bandwidth.
Now, while the flexibility and miniaturization characteristics of the tramsission highway structure of tunneline offer a significant improvement over previous approaches, it has been found that the extremely high precision with which the apertures for module pin connections must be patterned in the support board has prevented practical application of tunneline to a wide spectrum of microwave component support and interconnect structures.